Like other diseases for which there is no cure, chronic kidney disease takes an ever-increasing toll on patients who have it. As the disease progresses, the kidney becomes less efficient at removing various ions from the blood. Among these ions is phosphate, which can form insoluble particles when combined with calcium. In end-stage renal disease, the final stage of chronic kidney disease, kidney function is so compromised that phosphate levels in the blood (serum) become markedly elevated. This condition, known as hyperphosphatemia, carries with it many grave health risks. For example, when serum phosphate and calcium levels are above a certain threshold, hardened deposits may form throughout the body, endangering circulation. It is therefore very important to control serum phosphate levels in patients with end-stage renal disease.
Patients with end-stage renal disease may be advised to eat a diet low in phosphate. However, phosphate is present at some level in almost all the foods we eat. For this reason, phosphate binders were developed. Phosphate binders are compounds taken orally and which act in the gastrointestinal tract to bind phosphate and keep it from being absorbed. Phosphate binders are generally taken with each meal. Phosphate binders known in the art include, for example, various salts of aluminum and calcium, as well as some chemically synthesized crosslinked polymers. There are clinical circumstances in which the administration of aluminum or calcium salts is ill-advised. In animal models, certain crosslinked polymers carry with them elevated risks of carcinogenesis.